Engine starters often include mating elements that allow the transmission or torque from the starter motor to the starter pinion to transmit a torque generated from the starter motor to the rotating engine component that is engaged to the starter pinion. These elements typically provide an overrunning capability that allows torque to be transmitted from the starter motor to the starter pinion, but not from the starter pinion to the starter motor. In this manner, the starter motor can rotate the starter pinion, typically engaged to a flywheel or other rotating gear coupled to a crankshaft or turbine shaft. When the engine starts, the velocity of the rotating gear on the engine increases radically, to a speed much faster than the rotating starter can withstand. To prevent the starter from self-destructing due to this high velocity, these torque transmitting elements prevent the engine from applying a torque to the starter motor. A sprag clutch is one element commonly used as the torque transmitting elements in such applications as reciprocating internal combustion engines or the like.
Sprag clutches are usually in the form of a first shaft member coupled to the starter motor, and a second hollow cylindrical member attached to the starter pinion. Sprags, or oblong elements, are disposed circumferentially around the gap between the shaft member and the inside of the hollow cylindrical member such that they wedge between the inside of the hollow cylindrical member and the pinion when the pinion is rotated in a first direction with respect to the hollow cylindrical member, and are released when the shaft member is rotated in the opposite direction with respect to the hollow cylindrical member. Thus, the motor will wedge the sprags between the shaft member and the hollow member until the engine starts, at which time the hollow member, driven by the now-started engine, will increase in speed until it rotates faster than the shaft member, and the sprags will be released.
A drawback of this design is the need for a thick, and hence relatively massive hollow cylindrical member. This member must be thick to withstand the forces acting outwardly against the hollow member by the sprags during starting, and to withstand the centrifugal forces generated when the engine rotates the starter pinion after starting.
One method of improving upon this design is to insert a bendix in the mechanical train between the sprag clutch to cause the starter pinion to be moved back and away from the rotating gear on the engine when the engine starts. This design requires an additional element to the arrangement, however, the bendix.
What is needed is a simple apparatus for preventing torque transmittal from the gear on the engine to the starter motor that eliminates the need for a sprag and bendix. It is an object of this invention to provide such an apparatus.